1. Field of the Invention
This invention relates to compositions which are useful for preventing or destroying foam in aqueous systems and to a method of preparing them.
2. Description of the Prior Art
Water is widely used in various industries as a medium in which materials are temporarily suspended or dissolved during processing. These water slurries or solutions almost always contain surface active compounds either purposely added or as by-products. When such aqueous systems are subsequently subjected to violent agitation, as by mechanical shear, filtering or boiling, they tend to entrain air. The filter washing of pulp slurries in paper mills, the pumping of cement slurries, the shaking of a can of latex paint and the application of an aqueous coating with a roller, blade or brush are some of the more common situations where foam decreases the efficiency of a process and/or produces an unacceptable product.
Dispersions of solid particles in water insoluble organic liquids have been widely used for controlling foam in aqueous systems. Such dispersions usually employed agents to facilitate the spreading of the dispersions at the interface of the aqueous system with air. Anionic, cationic and nonionic surfactants were used for this purpose. These surfactants included such diverse materials as fatty acid soaps, amine salts, polyethylene oxide condensation products, polyethylene glycol esters and silicone oils. These spreading agents, although they increase the cost of a defoamer, often produce undesirable side effects, e.g., a loss of defoaming ability or an increase in viscosity when the defoamer is heated or stored for long periods of time. There is a definite need for defoamer compositions which do not lose defoaming ability or exhibit an increase in viscosity when the defoamer composition is heated at elevated temperatures or stored for long periods of time.